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George Herold George Herold is offline
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Default Re-winding solenoids.

On Oct 20, 4:31*pm, George Herold wrote:
On Oct 16, 4:48*pm, Jeffrey Angus wrote:

Just a few abstract thoughts here. It makes sense to me,
but then I've been known to over look the obvious on
occasion. ;-)

I have a solenoid coil that actuates a large 3-pole
contactor. A short pulse to pull up on a lever that
will toggle it from on position to another, and back.

Making measurements of the solenoid coil, although
potted in epoxy, yields a few measurements and a
couple of guesses.

Coil form 1" diameter, 1-3/8" width and 1.5" depth.
Going backwards on a solenoid coil java script, yields
a matching 125 mH inductance (as measured) and 95 ohm
DCR (as measured) for 2500 turns of #30 AWG which will
fill the bobbin.

This a 480 VAC actuator.

Am I headed in the right direction if I assume the key
factor here is ampere turns?

Not allowing for the added inductance by a movable core,
this has an impedance of roughly 100 ohms. So that works
out to 4.8 amps or 12,000 ampere turns.

Substituting 2000 turns of #28 AWG yields 80 mH, and 42
Ohms. And subsequently roughly 12,000 ampere turns at
240 VAC.

Putting 240 VAC across the 480 VAC coil yields only 6,000
ampere turns and obviously is NOT enough to actuate the
contactor transfer mechanism.

The reason I'm curious is that ASCO seems to think that
the replacement coil for this is worth $585, although
they will sell it as the "sale price" of only $421.80.

The other other one

"Everything from Crackers to Coffins"

Hi Jeff, *I know nothing about power stuff or soleniod coils. *I have
made a few open air magnetics. (Usually Helmholtz things) If the size
of both air coils is the same, then I believe your calculations are
correct. *It's only the magnetic field strength that you need to match
and that's proportional to number of amp-turns. *Wind away I say!

Driving home, I was thinking that since you're doing a pulsed thing
you may care about the L/R time constant. (Is the pulse time much
longer than that?) Did 'your' program spit out inductance values
too? (Forgive me, I'm too lazy to look for them.) For 'thin' coils
you'd expect the inducatance (for the low voltage coil) to go down by
four and the resistance to go down by two, so a decrease of two in the
time constant... hardly seems like it would matter, unless somethng
else in the circuit is expectng it to take longer. For your fat coil
the change in time constant is likely even less.

George H.

George H.- Hide quoted text -

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